Alzheimer's disease (AD) is the most common form of dementia in the elderly population. Associated with AD is the defective processing of the amyloid precursor protein giving rise to the potentially neurotoxic, 40-42 residues encompassing amyloid beta peptide (Aβ). Subsequent aggregation of Aβ to oligomers and long fibrils plays a pivotal role in the course of the disease, culminating in the formation of senile plaques (Haass and Selkoe (2007) Nat. Rev. Mol. Cell. Biol. 8, 101-112). Despite the increasing significance of AD there is still an unmet need for effective therapies to prevent, cure or decelerate this dementia.
Current anti-amyloid approaches aim at (i) the prevention of Aβ formation, (ii) blocking of its aggregation, (iii) reduction of soluble Aβ levels in the brain, and (iv) disassembly of existing amyloid plaques. So far, immunotherapies, comprising both active and passive immunization of AD patients, have been most promising in this field (Dodel et al. (2003) Lancet Neurology 2, 215-220; Lichtlen and Mohajeri (2007) J. Neurochem. 104, 859-874; Brody and Holtzmann (2008) Annu. Rev. Neurosci. 31, 175-193). However, recent clinical trials with active immunization of AD patients were ceased due to the incidence of meningoencephalitis in 6% of the patients. Due to these potential adverse side effects of Fc-mediated immunological functions, non-Ig binding reagents, such as Anticalins, provide an alternative. The identification of an Affibody molecule with specificity for amyloid beta is one example to illustrate the potential of engineered non-Ig binding proteins (Grönwall et al (2007) J. Biotechnol. 128, 162-183; Hoyer et al. (2008) Proc. Natl. Acad. Sci. USA 105, 5099-5104).
However, the bacterial origin of Affibodies may cause problems with immunogenicity in human patients.
Fibronectin (FN) plays an essential role in cell adhesion, migration, proliferation, and differentiation. FN is a large, modular, dimeric glycoprotein comprising multiple domains of type I, II, and III. Alternative splice variants of FN such as its extra-domain B (ED-B), which is incorporated between the FNIII7 and FNIII8 domains, are expressed in a tissue-specific and developmental stage-dependent manner (Zardi et al. (1987) EMBO J 6, 2337-2342).
ED-B is absent from normal adult tissue except during wound healing and neoplastic vascularization. Consequently, ED-B containing fibronectin is abundantly expressed in many different tumor types that attract neovascularization and undergo aberrant angiogenesis. While the actual biological function of ED-B in angiogenesis remains elusive, its incorporation into FN serves as excellent marker for tumorgenesis. Generally, discrimination between malignant tissues and healthy organs is an advantageous therapeutic strategy as the selective targeting of drugs directly to the tumor tissue leads to an increased local drug concentration.
In order to specifically detect and target ED-B, recombinant antibody fragments were raised using phage display antibody technology. One of the isolated antibody fragments is the L19 single chain Fv (Carnemolla et al. (1996) Int. J. Cancer 68, 397-405; Ebbinghaus et al. (2004) Curr. Pharm. Des. 10, 1537-1549). Addressing ED-B by L19 in combination with an effective cytotoxic agent currently shows prospects for cancer therapy and diagnostics (Schliemann and Neri (2007) Biochim. Biophys. Acta 1776, 175-192; Kaspar et al. (2006) Int. J Cancer 118, 1331-1339).
However, the L19 scFv fragment is prone to oligomerization.
Due to the above remaining problems in the treatment of Alzheimer's disease and the diagnosis or therapy of tumors, it is an object of the present invention to provide alternative methods and compounds which can be used in the treatment of Alzheimer's disease and the diagnosis or therapy of tumors.